Consolidation of carbon fiber laminae during polymer-matrix composite fabrication, studied by electrical resistance measurement

The consolidation of carbon fiber epoxy-matrix laminae during composite fabrication by lamination (involving consolidation, curing and cooling) was found to be hastened and to occur to a greater extent by increasing the pressure. The consequence of better consolidation remained after curing and subsequent cooling. A higher pressure resulted in a lower through-thickness resistivity in a composite after curing and cooling. The extent of consolidation was quantitatively described by N/N_o (the ratio of the number of fiber-fiber contacts between adjacent laminae at a given time, divided by that at the start of consolidation), which was calculated from the measured through-thickness electrical resistivity. From the variation of N/N_o during heating in the process of consolidation, three stages of consolidation were observed. In the first stage, N/N_o increased very gradually; in the second stage, N/N_o increased abruptly; in the third stage, N/N_o increased at a moderate rate.